Sails for sailcraft, which must have a three-dimensional curvature to be efficient (to “catch the wind”), are traditionally fabricated by sewing together a plurality of fabric panels cut out so that assembling them produces a three-dimensionally curved sail. Considerable work is required to compute the shape of the panels, mark them out, cut them out, apply glue and assemble the panels by sewing them together. Because this is labor intensive, the result is uncertain and often subject to errors. Also, the quality of sails made in this way leaves something to be desired, the seams creating points of weakness from which tears can start because of the holes made by the needle of the sewing machine.
The document EP-056 657-A discloses a three-dimensionally curved single-piece sail consisting of a single piece of flexible thermoplastics material sheet, possibly reinforced with thermoplastics polymer fibers. It describes a method of fabricating a sail by holding a continuous sheet of thermoplastics material, possibly reinforced with thermoplastics polymer fibers, by its edges, heating the sheet, applying pressure to the heated sheet to shape it by stretching it selectively, and cooling it. It states, without giving further details, that the sheet material is stretched by application of pressure over a mold or a curved shape, i.e. a convex molding surface.
Finally, the documents EP-475 083-A and WO-01/00487-A disclose laminated material sails made on a convex mold surface, either by successively depositing a flexible first sheet, continuous filaments, and a flexible second sheet, and laminating the combination on the mold surface, or by successively depositing two layers each formed of a plurality of sheets reinforced with filaments, with the edges of the panels of the two layers offset, and laminating the combination on the mold surface. According to the document EP-475 083-A, the mold surface whose shape corresponds to the shape of the sail to be fabricated is defined by rows of members with an appropriate profile mounted on parallel flexible battens, each of which is supported along its length by adjustable height columns supported by crossmembers of a supporting framework. These fabrication techniques entail time-consuming and sophisticated manual handling of costly fibers and make use of devices lacking in flexibility, and for this reason sails made in this way are restricted to top of the range racing craft.